The Institute of Medicine recently estimated that between 35,000 and 70,000 Americans annually require either permanent circulatory assist devices or cardiac transplantation. For these patients, the therapy of choice remains cardiac transplantation. However, the donor heart supply is severely limited (1,673 cardiac transplants were performed in the United States in 1989) and is expected to remain so into the foreseeable future. Thus, development of circulatory assist devices is critical to the survival of most of these heart-failure patients.
For the last 25 years, much of the work to develop circulatory assist devices has involved pulsatile pumps that mimic the pumping action of the natural heart. Impressive progress has been made in solving the complex problems associated with the safe delivery of blood to the systemic circulation. In fact, several systems are now successfully being used to support terminal cardiac patients who await transplantation. One such device, the Novacor left ventricular assist system (LVAS), has been used to support more than 100 heart-failure patients awaiting transplantation. FIG. 1 is a simplified diagnostic illustration of a LVAS shown implanted in a patient. LVAS 10, employed as a temporary bridge to cardiac transplantation, is coupled to the left ventricle 12 of a human heart 14 and includes an inflow conduit 16, an outflow conduit 18, and a pump/drive unit 20. Respective inflow and outflow valves are located at the connection of the inflow and outflow conduits 16, 18 to the heart's left ventricle 12, although these valves are not shown in the figure for simplicity. LVAS 10 is disposed below the user's diaphragm 22, with the inflow and outflow conduits 16, 18 passing through the diaphragm. Incorporated in LVAS 10 is a microprocessor-based controller for regulating the pumping of blood within the pump/drive unit 20.
Blood-biomaterial interactions are of critical importance to the operation of the LVAS implant. Undesirable formation of thrombus on biomaterial surfaces can lead to critical, sometimes fatal, results. This activation is likely a strong function of patient-dependent factors and the choice of biomaterials, but fluid-dynamic properties of the device are also of great importance. Although the conditions that cause activation are not completely understood, it is believed that high shear rates, areas of flow stasis, and generation of strong recirculation zones are undesirable within any blood contacting device. Understanding fluid flow within the LVAS implant is essential for improving its performance in increasing survivability and enhancing the health of implant users.
The present invention is a significant advance in the area of artificial organs in that it permits observing and measuring in great detail flow fields within an artificial organ such as a LVAS implant and in particular near the biomaterial surfaces within the artificial organ. The present invention has also been successfully applied to analyze flow within the Nimbus AXIPUMP (another type of LXAS) and a type of artificial lung called an intravenous membrane oxygenator. Although disclosed primarily in terms of the analysis of blood flow within an artificial implant organ, the present invention is not limited to this environment, but is equally applicable for the analysis, measurement and recording of fluid flow fields in virtually any transparent fluid transporting device or system.